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pneumatic problem

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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pneumatic problem

Unread postAuthor: scatdawg » Mon Apr 23, 2007 5:59 pm

need some ideas and help on what has gone wrong with my cannon. its a coaxial. after assembling the thing, it shot great for a for about 50 or so shots. then air started leaking out the barrel so i figured the rubber seal on the piston must have failed. i took it apart and found it was badly worn. i replaced the rubber exactly as it was before. now it seals the barrel again but it seems like its not venting fast enough to move the piston back now. i dont understand why it wont work now. i added some foam behind the piston to lessen the pilot volume to no avail. i was wanting some input on whether my design may have flaws. the barrel i.d. is .800 and the chamber i.d. is 2.5 inches. my piston is 2.495 diameter 1.625 in lenght with two o-rings. it seals and slides perfect. the lenght behind the piston to the bumper is .750 inch. ive been shooting at 140psi with no problems until the rubber wore out. i have a ball valve in front of a quick disconnect attached to the compressor and i vent the pilot with a highly modded air gun. venting with the gun or the ball valve produces the same result. weak fire and large exhaust from the pilot. any input or suggestions would be greatly appreciated.
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Unread postAuthor: ShowNoMercy » Mon Apr 23, 2007 6:01 pm

Is the pilot area gunked up and not allowing the piston to slide well? You could try washing it and then putting some sort of lube on it to prevent that from happening. If thats not it, well I dont know, but have hope, if it worked at first then it will work later.
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 23, 2007 6:07 pm

Worn piston o-rings?
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Unread postAuthor: rad14701 » Mon Apr 23, 2007 6:11 pm

Can you fill the gun and then remove the quick disconnect nipple from the ball valve and then test fire the gun...??? If you are using the smaller version of the air coupler components you could end up with ball valve performance worse than that of the blow gun... I've had similar performance problems with air tools...
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Unread postAuthor: scatdawg » Mon Apr 23, 2007 8:09 pm

sorry it took so long ro reply,... wife stole the computer. i did replace the o rings. still no good. i will try tommorow to remove the quick connect and try firing with un restricted ball valve. its just really puzzling as to why it wont fire now. also i did clean the area where the piston slides and re-lubed the o rings. while away from the computer i swapped out to my 2.497 piston without orings and this didnt help either.
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 23, 2007 10:53 pm

Have you changed your filling pattern? Are you leaving it long enough for the chamber to fill up to its full pressure? Have the chamber or piston somehow been distorted by repeated firing and don't fit as well as they used to? Other than that I can't see a reason why performance should have changed.
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